docs: def evaluate_perceptron(ctx, model, corpus):
      """Evaluate performance of Averaged Perceptron POS Tagger."""
      click.echo('chemdataextractor.pos.evaluate')
      if corpus == 'wsj':
          evaluation = wsj_evaluation
          sents = list(evaluation.tagged_sents())
          for i, wsj_sent in enumerate(sents):
              sents[i] = [t for t in wsj_sent if not t[1] == u'-NONE-']
      elif corpus == 'genia':
          evaluation = genia_evaluation
          sents = list(evaluation.tagged_sents())
          # Translate GENIA bracket tags
          for i, genia_sent in enumerate(sents):
              for j, (token, tag) in enumerate(genia_sent):
                  if tag == u'(':
                      sents[i][j] = (token, u'-LRB-')
                  elif tag == u')':
                      sents[i][j] = (token, u'-RRB-')
      else:
          raise click.ClickException('Invalid corpus')
      tagger = ChemApPosTagger(model=model)
      accuracy = tagger.evaluate(sents)
      click.echo('%s on %s: %s' % (model, evaluation, accuracy))